Protective housing for a ceramic actuator

ABSTRACT

A housing that protects a ceramic actuator from excessive and damaging displacement comprises a protective structure arranged to limit the motion of the actuator by contacting at least one section of said actuator between fixed and moving terminals of said actuator. A suspension system for a lens holder of a miniature camera actuated by a ceramic actuator comprises four pivotally connected link elements in form of a parallelogram connected between a housing and the lens holder.

This invention relates to actuators in particular ceramic actuatorswhich may be electro-active, for example piezoelectric. In one aspect,this invention relates to a housing for such actuators which may beapplied to a camera in which the actuator moves a lens holder. Inanother aspect, this invention relates to a suspension for a camera inwhich the actuator moves a lens holder. Both aspects may be applied tomicro-cameras in portable data processing or communicating devices.

Piezoelectric and other electro-active benders made from ceramic basematerial such as lead zirconate titanate (PZT) are used in manyapplications. They are manufactured for example from multilayer (green)material and sintered at high temperatures into their final shape.

A variety of configurations for such actuators are known. Comparablylarge translation displacements have been recently achieved by using astructure of piezoelectric bender tape extending helically around anaxis which is itself curved, as described, for example, in WO-0147041 orD. H. Pearce et al., Sensors and Actuators A 100 (2002), 281-286. Suchdevices are capable of exhibiting displacement in the order ofmillimetres on an active length of the order of centimetres.

Whilst the manufacturing of ceramic actuators is known, theirapplicability is limited due to the brittleness of the material they aremade of. It would therefore be desirable to provide housing for ceramicactuators that reduces the sensitivity of ceramic actuators againstsudden impacts as caused for example by a drop onto a hard surface.

As a separate matter, in recent years, with the explosive spread ofportable information terminals called PDAs and portable telephones, anincreasing number of products incorporate a compact digital camera ordigital video unit employing a CCD (charge-coupled device) or CMOS(complementary metal-oxide semiconductor) sensor as an image sensor.When such a digital camera or the like is miniaturized using an imagesensor with a relatively small effective image-sensing surface area, itsoptical system also needs to be miniaturized accordingly.

To achieve focussing or zooming, additional drive motors have to beincluded in the already confined volume of such miniature cameras.Whilst most of the existing cameras rely on variations of the well-knownelectric-coil motor, a number of other actuators have been proposed assmall drive units for the lens system. These novel drive units ofteninclude actuators of electro-active material, for example piezoelectric,piezoresistive, electrostrictive or magnetostrictive material, typicallyceramic actuators.

Small electro-active actuators with comparably large translationdisplacements have been recently build using a structure ofpiezoelectric bender tape extending helically around an axis which isitself curved, as described, for example, in WO-01/47041 or D. H. Pearceet al., Sensors and Actuators A 100 (2002), 281-286. Such devices arecapable of exhibiting displacement in the order of millimetres on anactive length of the order of centimetres. They may be manufactured frommultilayer ceramic base material such as lead zirconate titanate (PZT)and sintered at high temperatures into their final shape. The use ofsuch actuators as drive motors for lens systems has been proposed inWO-02/103451.

As drive units adapt to the reduced volume of the compact cameradesigns, lens suspensions systems, which constrain the motion of thelens holder, have to co-evolve. Lens suspension systems suitable forminiaturized cameras, particularly for cameras driven by anelectro-active transducer ideally have a low stiffness, resistive forceor friction in direction of the desired motion and high stiffness in allother directions.

According to a first aspect of the invention, there is provided ahousing for a ceramic actuator including a protective structure,preferably with compliant elements contacting the actuator, limiting thethe range of motion of sections of the bender located distant from bothfixed and moving terminals of the bender.

An actuator is typically operated with a fixed terminal or end sectionand a moving terminal or end section. The fixed terminal is attached tothe housing or mounted on a base structure shared with the housing. Themoving terminal of the actuator is the section of the actuator thatdisplays the largest displacement relative to the fixed section of theactuator. It is seen as an important feature of the first aspect of theinvention that the protective structure is adapted to limit the range ofdisplacement of the actuator by contacting the actuator at one or moresections located between the two terminal sections of the actuator.Thus, the actuator is free to move, on actuation, within the range ofdisplacement until it contacts the protective structure and referencesto contacting should be understood accordingly. Such a protectivestructure protects the actuator against a sudden impact, as caused forexample by a drop onto a hard surface, by preventing excessivedisplacement of the actuator which would cause damage.

The actuator may be a linear actuator having a moving end section thatdescribes a near linear motion.

Advantageously, the protective structure is placed outside the nominalrange of displacement. The nominal range of displacement of the actuatoris the displacement exhibited by the actuator during normal operatingconditions. The limits of the nominal range of displacement define asurface or an envelope outside which the protective structure islocated.

Advantageously, the protective structure follows the contour defined bythe limits of the nominal range of displacement. For example, theprotective structure may be arranged to have an approximately constantdistance from the limits of the nominal range of displacement atdifferent points along the actuator.

In one type of embodiment the protective structure includes one, two ormore discrete elements adapted to contact the actuator, for exampleresilient members such as mechanical spring type structures for removalof energy from the actuator on impact. Suitable structures include forexample resilient beams disposed along the protective structure.

In another type of embodiment the protective structure includes acontinuous surface adapted to contact a section extending along theactuator.

Desirably, the portions of protective structure adapted to contact theactuator are compliant, for example by being resilient or by beingformed by compliant material, so as to be capable of absorbing thekinetic energy of the actuator.

The protective housing of the invention may be readily manufactured forexample by moulding of plastic materials. The protective structure maybe advantageously moulded in one piece with the housing. The compliantlayer, if provided, may be attached for example by glueing to theprotective structure. Alternatively, the compliant layer or layers maybe incorporated in the housing during manufacture by two-shot moulding,in which the housing and compliant layers are produced in differentmaterials within the same mould. Resilient structures such as resilientbeams may be advantageously moulded in one piece with the housing,forming the appropriate ramp contour. Alternatively, spring structuresmay be cut from thin metal sheet, for example by photo-chemical etching,bent to the appropriate shape if necessary, and then fixed into thehousing, preferably by means of moulded locating pips in the housing.

The present invention is particularly advantageous used to houseactuators capable of relatively large displacement, such as theactuators of the type mentioned above and disclosed in WO-0147041 or D.H. Pearce et al., Sensors and Actuators A 100 (2002), 281-286, becausesuch actuators are particularly susceptable to damage from a suddenimpact.

According to a second aspect of the invention, there is provided acamera including a support structure; a lens holder holding at least onelens; a suspension for mounting said lens holder on the supportstructure; and an actuator for moving said lens holder, wherein thesuspension includes two link elements each pivotally connected to thesupport structure at one end and pivotally connected to the lens holderat the other end.

Such a suspension has a low stiffness, resistive force or friction inthe direction of the desired motion and high stiffness in all otherdirections. It is thus suitable for miniaturized cameras, particularlyfor cameras driven by an electro-active actuator.

The suspension system is preferably a type of a four-bar linkage, inwhich the suspension further includes a first attachment member to whichthe first end of each link element is pivotally connected and which isattached to the support structure, and a second attachment member towhich the second end of each link element is pivotally connected andwhich is attached to the lens holder. Such a type of suspension systemcan be formed from one continuous piece of material, preferably aplastics material, for example selected for example from a groupincluding polypropylene, polyethylene and polyamide (nylon).Advantageously, the thickness of the link element tapers towards thepivotally connected ends such that the link element is thicker in themiddle than in the immediate vicinity of the pivots or hinges.

Advantageously, the pivotally connected ends of the suspension extendalong the circumference of the lens holder.

Preferably, the pivotally connected ends of the suspension extend alonga length which exceeds a tenth, more preferably a third or even a half,of the diameter of the lens holder. This provides the advantage that, ascompared to a suspension where this length is shorter, the suspensioncan sustain a higher torsional force without significant deformation.

In a preferred embodiment the actuator extends around the lens holderleaving a single gap with the suspension located in said gap. In thisembodiment, the suspension supports the lens holder at just one side orrelative to a cylindrical lens holder within just one sector. Thesector, measured by connecting the end points of the longest pivot thatis located at the lens holder with the center of the lens holder, ispreferably less than 90 degrees. As a result, the lens holder issuspended at a quarter or less of its circumference—excluding thesuspension effected by the actuator.

In some variants of the invention it may advantageous to limit theamount of rotational motion around the pivoting ends to less that 20degrees, because, as a result, the lens holder's motion is limited tothe equivalent maximum displacement which improves the protection of theactuator.

These and other aspects of inventions will be apparent from thefollowing detailed description of non-limitative examples makingreference to the following drawings.

In the drawings:

FIG. 1A is a schematic cross-section of a ceramic bender in a housing inaccordance with an example of the present invention;

FIG. 1B is a schematic cross-section of a ceramic bender in a housing inaccordance with another example of the present invention;

FIG. 2A is a schematic cross-section of a super-coiled bender carrying alens system in a housing in accordance with an example of the presentinvention; and

FIG. 2B is a schematic partial top view of a super-coiled bendercarrying a lens system in a housing in accordance with an example of thepresent invention;

FIG. 3 is a schematic cross-section of a super-coiled bender carrying alens system in a housing in accordance with an example of the presentinvention;

FIG. 4 is a schematic perspective view of a protective structureincorporating compliant beam protrusions in accordance with an exampleof the present invention;

FIG. 5 is a schematic perspective view of a protective structureincorporating compliant fingers in accordance with an example of thepresent invention;

FIG. 6 is a schematic perspective view of a protective structureincorporating shaped compliant fingers in accordance with an example ofthe present invention;

FIG. 7 is a schematic perspective view of a protective structureincorporating compliant cupped fingers in accordance with an example ofthe present invention.

FIG. 8A is a perspective view on a camera housing;

FIG. 8B is a perspective view on the camera housing of FIG. 8A with atop lid removed; and

FIGS. 9A and 9B are perpendicular schematic cross-section of the camerahousing of FIG. 8.

In FIG. 1A, there is shown a schematic vertical cross-section through ahousing 10. Within the housing 10 there is mounted a layeredpiezoelectric bender 11 having a conventional structure comprising twolayers of piezoelectric material with electrodes (not shown) which inuse receive an activation voltage which causes a differential change inlength of the two layers concomitant with bending of the bender 11. Afirst end 111 of the bender 11 is fixed to the housing. At the distalend 112 of the bender 11, a load 12 is attached to the bender 11. Adouble arrow 13 indicates the direction in which the distal end 112 ofthe bender 11 moves when the bender 11 is activated. The dashed lines141, 142 indicate the upper and lower limits, respectively, of thenominal displacement of the bender 11, that is the displacementexhibited by the bender 11 during normal operating conditions.

A novel feature of the housing are six protective elements 15 whichtogether form a protective structure for the bender 11. The elements 15extend from the housing 10 to points close to the dashed lines 141,142that indicate the limits of the nominal displacement. The elements 15are posts or blades carrying a compliant foam layer 151 at locationsfacing the bender 11 that would first come into contact with the movingbender 11.

As the bender 11 in the housing 10 is subject to an impact force, theinertia of the combined mass of bender 11 and load may force the bender11 to move beyond the nominal limits of displacement, thus precipitatingcracks in the ceramic material of the bender 11. The support elements15, however, are designed and placed such that the bender 11 contacts atleast one of the elements before a damage to the ceramic materialoccurs. Kinetic energy stored in the bender 11 is then absorbed by thefoam elements 151.

In FIG. 1B, there is shown a similar configuration to the one of FIG.1A. In this variant, however, the protective structure 15 takes adifferent form and in particular is laterally extended to form acontinuous surface contoured to follow approximately the nominaldisplacement envelope 141, 142. A foam layer 151 protects the bender 11from the impact of a sudden contact with the protective structure 15, asin the example of FIG. 1A.

FIGS. 2A and 2B show a camera assembly having a protective housing 20,shown in both a vertical cross-section (FIG. 2A) and a horizontalcross-section (FIG. 2B).

In this example, the actuator 21 comprises a piezoelectric multi-layer,bender tape, for example of a bimorph construction, extending helicallyaround an axis which is itself curved, as described, for example, inWO-01/47041 or D. H. Pearce et al., Sensors and Actuators A 100 (2002),281-286 which are both incorporated herein by reference and theteachings of which may be applied to the present invention. Inparticular, the actuator 21 comprises a tape wound helically around afirst axis, referred to as the minor axis. The helically wound portionis further coiled into a secondary winding of about three quarters of acomplete turn. The axis of this secondary winding is referred to as themajor axis. The first winding is known as the primary winding or primaryhelix. Although in this embodiment the secondary winding is aboutthree-quarters of a complete turn, in general, the secondary windingcould be any curve and could exceed one turn and form a spiral orsecondary helix. It is therefore usually referred to as secondary curve.The tape is arranged on actuation to bend around the minor axis. Due tothe helical curve around the minor axis, such bending is concomitantwith twisting of the actuator 21 around the minor axis. Due to the curvearound the major axis, such twisting is concomitant with relativedisplacement of the ends 211, 212 of the actuator 21.

The proximate end 211 of the actuator 21 is fixed to the housing 20.Onto its distal end 212 there is mounted a lens barrel 22 at theapproximate center of the housing. Consequently, actuation of theactuator 21 drives movement of the lens barrel 22 relative to thehousing 21. This type of lens suspension and actuations system aredescribed in greater detail in WO-02/103451 and WO-03/048831, which areboth incorporated herein by reference and the teachings of which may beapplied to the present invention.

The housing of the present example includes a protective structure 25 inthe form of two sloping surfaces or ramps arranged above and below theactuator 21 approximately following the contours of the upper and lowerlimits, respectively, of the nominal displacement of the actuator 21,that is the displacement exhibited by the actuator 21 during normaloperating conditions, thereby limiting the motion of the actuator 21.This protective structure 25 is covered with foam layers 251 facing theactuator 21 so as to come into contact with the moving actuator 21.

The housing 20 has end stops 201 arranged to limit the motion of thelens barrel 22. Thus, with the occurrence of an impact, when the lensbarrel 22 hits the end stops 201, the actuator 21 can be regarded asbeing momentarily fixed to the housing 20 at both ends. Between both nowfixed ends 211,212, however, the remaining sections of the actuator 21continue to move, thus potentially causing, in the absence of theprotective structure 25, damage to its ceramic material. As however theactuator 21 with its middle section contacts the protective structure25, the motion of the actuator 21 is limited and the kinetic energy ofthe actuator 21 is absorbed by the foam layer 251, so the risk of damageis consequently reduced.

The protective structure 25, 251 is shaped such that, in the event of animpact, the actuator 21 contacts approximately evenly along its length.In the example, it bends into half a turn above and below the secondaryturn of the actuator 21. The contact surface 251 of the protectivestructure may be shaped convex to provide a broader area of contact withthe outer circumference of the actuator. The advantage of a continuousor quasi-continuous support is shown by reference to the following tablewhich, for the case of a protective structure of discrete elements,lists the length of actuator sections between the discrete elements (orin other words the relative separation between neighboring discreteelements) and the maximum stopping force that can be applied to theactuator section before causing damage to it. Length of unsupportedsections between two supports Maximum Force Distance (relative units)(N) (mm) 4 0.35 7.3 3 0.46 4.1 2 0.7 1.8 1 1.4 0.45

From the table, the stopping distance can be calculated. It is apparentfrom the table that closer points of contact, and in the limitcontinuous contact, is better to stop the actuator before it reaches itsbreaking point.

FIG. 3 shows a vertical cross-section of a further camera assembly in aprotective housing. This camera assembly is similar to that of FIGS. 2Aand 2B, so common elements are given the same reference numerals and adescription thereof is not repeated. The camera assembly has an actuator21 of the same type as in FIG. 2A. The actuator 21 is attached to a lensbarrel 22 and to a housing (attachments not shown) which in this casecomprises two parts, namely a bottom housing 26 and a top housing 27. Atransparent cover 221 and image sensor 222 are shown above and below thelens barrel in the top and bottom housings 27,26 respectively. In thehousing parts 26,27, a protective structure 25 takes the form of slopingsurfaces or ramps which follow the actuator 21 from above and below andare faced with compliant material 251. Additional protection is providedat the inside of the bottom housing 28 in the form of compliant pads281, to afford protection against sideways motion.

Each part 26, 27 of this housing may be manufactured by a two shotmoulding process, in which the housing parts 26, 27, and the compliantmaterial 251 and the compliant pads 28 are formed together in the samemoulding process For example, the top housing 27 may be produced byfirst forming the compliant pads 251 by a first shot of resin into asuitable mould, and then forming the housing 27 on top of the pads 251with a second shot of (different) resin. Similarly, the bottom housing26 may be moulded in two shots, one for the compliant pads 251,281 andone for the more rigid housing structure 26.

FIG. 3 also shows further protection for the lens and actuator system,in the form of end stops 201 for the lens barrel, end stops 202 for thecomplete assembly, and a protective pad 203 around the lens barrel.These additional protective features may be moulded integrally with thehousing or lens barrel elements, as above. The assembly of FIG. 3provides comprehensive shock protection for its functional elements(actuator 21 and lens barrel 22) and can be readily and cheaply massmanufactured.

FIGS. 4 to 7 show perspective views of alternative protective structureswhich may be used in place of the protective structure 25 shown in FIGS.2 and 3. In particular, the compliant foam layer 251 of FIGS. 2 and 3 isreplaced by a plurality of discrete, resilient elements in the form ofmechanical spring structures, serving to remove energy from the movingactuator on impact. FIGS. 4 to 7 show the lower protective structure,the upper protective structure being a mirror image thereof.

FIG. 4 shows a partial perspective view of such a protective structure35 incorporating a spring structure 351 within a housing 30, forprotection of a ceramic actuator and lens barrel assembly (not shown)similar to those in FIG. 2. The spring structure follows the rampcontour already described and includes multiple compliant beamprotrusions, to contact the actuator on impact and remove energy.

FIG. 5 shows a partial perspective view of a further embodiment in whichthe spring structure 451 is a multitude of compliant beams or fingers,like a comb, along the ramp contour of the protective structure 45within a housing 40. The fingers 451 repeat along the whole length ofthe protective structure 45 although only a small number of fingers 451are shown in the drawing.

FIG. 5 shows a partial perspective view of a further embodiment in whichthe compliant beams or fingers of the spring structure 551 (on theprotective structure 55 in the housing 50) are an ‘S’ shape. This shapeallows allows the fingers to be longer than in the embodiment of FIG. 5.

FIG. 7 shows a partial perspective view of a further embodiment in whichthe compliant beams of the spring structure 651 are cupped such thatwhen they contact the coiled ceramic actuator (not shown) the load isdistributed over a greater area. The cups are designed to follow thecurvature of the surface of the ceramic actuator. The cupped fingers 651repeat along the length of the protective structure 65 within thehousing 60; in the drawing only 3 of the cupped fingers are shown.

The embodiments shown in FIGS. 2 to 7 are examples of compliantstructures and it will be apparent that other variations fall within thescope of the present invention.

In FIG. 8A, there is shown a camera housing 100 for a miniature camera.The housing 100 includes a top lid 101 with a central opening oraperture 102 for the passage of light from the exterior into theinterior of the housing 100. The opening can be covered by an opticalfilter. The lower section of the housing 100 includes a bottom lid 103and a base plate 104. The base plate carries the image sensor (notshown) which may be a CCD or CMOS device together with other circuits tocapture the image and transmit it to other parts of the camera.

At one side of the housing 100 there is shown an anchor plate 105 whichprovides mounting points for a suspension system to be described below.Another plate 106 is used to mount the fixed end 111 of a piezoelectricactuator 110.

To further protect the camera and the actuator, the housing 100 may becast into a block of suitable plastic material.

The housing 100 acts as a support structure for a lens holder 120 asfollows. FIG. 8B shows the housing 100 with the top lid 101 removed thusexposing the lens holder (or barrel) 120 with a first upper lens 121visible. The lens holder 120 has a nominally cylindrical shape that isflattened along one side 122 to provide a mounting surface for thesuspension 130. The lens holder 120 is axially movable relative to thehousing 100 to allow focusing.

The actuator 110 comprises a piezoelectric multi-layer, bender tape, forexample of a bimorph construction, extending helically around an axiswhich is itself curved, as described, for example, in WO-01/47041 or D.H. Pearce et al., Sensors and Actuators A 100 (2002), 281-286 which areboth incorporated herein by reference and the teachings of which may beapplied to the present invention. In particular, the actuator 110comprises a tape wound helically around a first axis, referred to as theminor axis. The helically wound portion is further coiled into asecondary winding of about three quarters of a complete turn. The axisof this secondary winding is referred to as the major axis. The firstwinding is known as the primary winding or primary helix. Although inthis embodiment the secondary winding is about three-quarters of acomplete turn, in general, the secondary winding could be any curve andcould exceed one turn and form a spiral or secondary helix. It istherefore usually referred to as secondary curve. The tape is arrangedon actuation to bend around the minor axis. Due to the helical curvearound the minor axis, such bending is concomitant with twisting of theactuator 110 around the minor axis. Due to the curve around the majoraxis, such twisting is concomitant with relative displacement of theends 111, 112 of the actuator 110.

The lens holder 120 is placed in the center of the actuator 110. Themoving end 112 of the actuator 110 is attached to the lens holder 120 ata point or area at mid-height of the lens holder 120, i.e., close to itsequator. Consequently, actuation of the actuator 110 drives movement ofthe lens holder 120 relative to the housing 100. This type of lenssuspension and actuation system is described in greater detail inWO-02/103451, which is incorporated herein by reference and theteachings of which may be applied to the present invention.

The fixed end 111 of the actuator 110 extends into a flat portion whichacts as a tab for connecting the actuator 110 to the housing 100. Thistab has electrical contact pads 113 on the bottom face, soldered ontocorresponding contact points on the board 106. Through these contactsexternal control signals or voltage levels are applied to the electrodesof the actuator 110.

The suspension 130 will now be described, with reference to FIG. 9Awhich is a cross-sectional view of the suspension 130.

The suspension 130 is a specific form of a four-bar linkage comprisingfour links pivotally connected together in the shape of a parallelogramas follows. The first link is a first attachment member 132 rigidlyconnected to the housing 101, 103. The second link is a secondattachment member 134 rigidly connected to the lens holder 120. Theremaining two links are two link elements 133, 135 which each extend,parallel to each other, between the first and second attachment members132, 134 and are pivotally connected to the first and second attachmentmembers 132, 134 as follows. The links 132-135 are integrally formedfrom a continuous piece of material. The thickness of the continuouspiece of material forming each link 132-135 tapers towards the portionswhich connect each adjacent pair of links 132-135, such that thematerial is reduced to a thin bridge connecting the two adjacent links132-135, whilst the middle section of each link 132-135 remainsrelatively stiff. As a consequence the suspension 130 and its links132-135 offer small resistance against motion of the lens holder 120 inthe desired (vertical) direction but much greater resistance againstmotion in other directions. The links 132-135 and, hence, the portionswhich connect each adjacent pair of links 132-135 have a width of about4 mm and the nominal diameter of the lens holder 120 is 9.5 mm, thuseffectively preventing a rotational or tilting movement of the barrel.

Each of the the portions which connect each adjacent pair of links132-135 extends linearly in the direction of its axis of relativerotation along the circumference of the lens holder 120, thus providingresistance to torsional forces which otherwise could lead to a tiltingof the suspended camera. The length of the portions which connect eachadjacent pair of links 132-135 in the above example is approximately athird to half of the diameter of the lens holder.

In the example, the suspension 100 is preferably made from a singlepiece of polypropylene. Other suitable plastic materials includepolyethylene or polyamide (nylon). Alternatively the bars of thesuspension can be made from metals or metal alloys. The suspension canbe cast or injection molded.

It will be appreciated that the lens holder 120 is suspended solely bymeans of the suspension 130 and the actuator 110. The system is free offurther potential sources of friction such as guide rails or posts toreduce the potential amount of force the actuator has to provide. It wasfound that even though the suspension 130 connects to the lens holder120 exclusively within a sector of less than 90 degrees, and both theactuator 110 and the suspension 130 are linked to the lens holder 120within a sector of less than 120 degrees, the tilt of the lens holder120 can be kept within the limits required to generate pictures in VGAor SVGA quality.

The camera assembly also has protective structures of the same type tothose described in FIGS. 2 and 3, as shown in FIGS. 9A and 9B, inparticular in the form of compliant polyurethane foam layers 108 gluedto inner surfaces of the housing 100 around the actuator 110. In themanner described above with reference to FIGS. 2A and 2B, the layers 108protect the actuator 110 from a sudden impact force, particularly if theforce accelerates the actuator 110 in a direction that is notconstrained by the suspension 130. In FIGS. 9A and 9B, this direction isthe vertical direction in the paper plane. The distance between theactuator 110 in its inactive state, and the foam layers 108 increasestowards the moving end of the actuator, so as not to interfere with thenominal displacement of the actuator during the normal operation of thecamera.

1-30. (canceled)
 31. A housing in which there is mounted a ceramicactuator which is a bender extending in a helix around an axis which iscurved, the housing having a protective structure comprising acontinuous sloping ramp having a compliant portion facing the actuatorand being arranged to limit the range of motion of said actuator bycontacting a middle section of said actuator between fixed and movingterminals of said actuator.
 32. A housing according to claim 31, whereinsaid sloping ramp is a rigid member, the compliant portion and the rigidmember being formed together in the same moulding process.
 33. A housingaccording to claim 31, wherein the protective structure is locatedoutside a nominal range of displacement of the actuator.
 34. A housingaccording to claim 31, wherein the protective structure is arranged tocontact the actuator at points along a contour defined by the limits ofthe nominal range of displacement of the actuator.
 35. A housingaccording to claim 31, further comprising a stop arranged to limitdisplacement of the moving terminal of the actuator.
 36. A housingaccording to claim 31, further comprising a lens system actuated by theactuator.
 37. A housing according to claim 31, wherein the compliantportion is a layer of compliant material.
 38. A housing according toclaim 37, wherein the layer of compliant material is a foam layer.
 39. Ahousing according to claim 37, wherein the surface of the layer ofcompliant material facing the actuator has a convex shape.
 40. A housingaccording to claim 31, wherein the compliant portion comprises aplurality of discrete resilient elements.
 41. A housing according toclaim 40, wherein the discrete resilient elements are mechanical springstructures.
 42. A housing according to claim 31, wherein the protectivestructure comprises two said continuous sloping ramps arranged onopposite sides of the actuator.